1. Field of the Invention
The present invention relates to a procedure for regulating the d.c. voltage of a pulse-width modulated rectifier bridge controlled by self-commutated semiconductor components.
Pulse-width modulated mains rectifier bridges are used to feed a constant-voltage load, which is connected to the d.c. terminals of the rectifier. Such a load may be e.g. an inverter provided with a constant-voltage intermediate circuit, used to feed an elevator motor. The characteristic features of such rectifiers include two-way power flow and, due to pulse-width modulation (PWM), low distortion levels for the currents in the supplying network.
2. Description of Related Prior Art
Previously known procedures are based on the use of phase voltages measured via transformer circuits to produce either the current references for a rectifier working on the principle of two-position control, or the voltage references for a PWM rectifier. In both cases, the disturbances materialized in the phase voltages are directly transmitted to the modulation references and therefore to the currents taken from the network. This involves a deterioration of the characteristics of the rectifiers, especially in industrial networks where as it is well known, the voltages are distorted. Moreover, when a two-position control is used the rectifier voltages and currents contain harmonics which extend over a large frequency range and are therefore difficult to filter. In addition, for both methods, each phase voltage requires its own regulation circuits, thus increasing the complexity of the systems.